Solid carbon dioxide product and method of and apparatus for making it



Sept. 19, 1933. c JONES ET AL 1,927,173

SOLID CARBON DIOXIDE PRODUCT AND METHOD OF AND APPARATUS FOR MAKING ITFiled March 28, 1929 Z21 1 15 INVENTORS C iiarlaa .Z JOnesz J56 220018Ml.

ATTORNEY Patented Sept. 19, 1933 UNITED STATES 1,927,173 SOLID CARBONDIOXIDE PRODUC'E. AND

METHOD OF AND APPARATUS FOR ING IT Charles L. Jones, Pittsburgh, Pa.,and

Small, New York, N.

MAK-

John D. Y., assignors to llryice Corporation of America, New York, N.Y., a

corporation of Delaware Application March 28, 1929.

11 Claims.

This invention relates to blocks of solid carbon dioxide having novelcharacteristics and qualities and to novel methods of producing suchblocks. These novel features are. the results of certain 5 discoverieswhich in turn have resulted from making blocks in accordance withpresent-day commercial practice, supplemented by exhaustive experimentalinvestigation, as will be evident from the following:

Solid carbon dioxide now in commercial use is made from very fine grittycrystals, produced by jet discharge and the rapid expansion of liquidcarbon dioxide to approximately atmospheric pressure, as, for instance,in apparatus like that set forth in Martin Patent No. 1,659,434. Thesefine crystals are ordinarily compressed into sandy snow-white blocks,usually cubes of relatively large size, say x 10 x 10, the size and theshape beinga compromise with a view to getting large volume per unit ofheat absorbing area, thereby to avoid excessive evaporation wastage,while also complying with the users requirement of shape and sizeconvenient for sawing into smaller sizes and shapes for specialpurposes. The present standard blocks weigh about '70 pounds per cubicfoot or, say, 40 pounds for the 10 inch cube. These or similar standardsof size, weight and shape are commercially approximated by having thefine grain crystals properly distributed in the mold and the gasexpelled therefrom by tamping before pressing, as set forth in MartinPatent No. 1,659,435, but such blocks fail to meet the usersrequirements, in certain particulars.

The user expects the block to be of standard density throughout so thatwhen sawed into pieces of given size and shape, all pieces will affordthe same amount of refrigerative work regardless of what part of theblock it is sawed from. He also expects the block to be tough so that itwill not break when being handled or shipped and will not crumble whenbeing sawed into small pieces. The present standard blocks, however, arenot of sufliciently uniform density, nor toughness and they rapidlydeteriorate, becoming crumbly and sand like, sometimes within a day ortwo after making.

Our investigations seem to show that this is because the block iscomposed of hard, gritty, minute crystals that afford frictionalresistance to transmission of pressure to the interior of the block;that have enormous surface area per unit volume and that have a largepercentage of voids between crystals. when the pressure is applied, thegritty particles seem to weld at their points of contact sufllciently toafford structural resistance to further compression before pressure canbe transmitted to the interior and more remote portions of the block. Inany event, it has been found practically impossible to eliminate theSerial No. 350,588

ourselves to details of theory, it seems to be a fact that in thepresent standard blocks, interior sublimation and outflow of gasfacilitates rapid deterioration of the interior to a crumbly condition,while refreezing of the down flowing or outfiowing gas increases thehardness and glassy brittle quality of other portions of the block,notably the exterior or other parts that are already densest.

Others have employed certain materials such as water ice and lowfreezing point liquids, with a view to lubricating the gritty particlesand also to afford a cement or binder between them, but such adulterantsare all objectionable, water because it is brittle when frozen and wetwhen melted, and the others for various reasons.

We have tried applying greater pressures, but the result is to increasenon-uniformity as well as density, probably due to the sandy, grittyquality of the fine crystals, which prevents proper transmission of theincreased pressure into the interior of the block. A thin layer of theblock, at the plunger-contacting face, becomes glassy and hard, but italso becomes very brittle. Under very great pressures such as a thousandpounds or more persquare inch, this brittle glassy formation may extendfurther inward, but it merges into a porous snow formation similar tothat of the present standard commercial blocks, although the grain maybe finer and the density greater. Using a relatively warm mold mayresult in similar vitrefaction of a thin skin on the other faces of theblock. Such high pressure composite blocks are uncommercial for ordinarypurposes, one objection being that they are of inferior toughness.Another is that when sawed in given sizes and shapes, the pieces are notstandardized, those from the denser portions being too brittle andhaving far more refrigerant value than those from the snowy portion.Another quite unexpected objection is that ordinary saws which operatesatisfactorily onproducts of relatively uniform density, either dense orporous, will break when used on the composite products. While wecontemplate sawing off the dense layer and using it as a separatecommercial product, it is evident that if these high pressure compositeblocks have ever been produced by others, either accidentally orexperimentally, they have not been used for commercial purposes, becausethey do not answer present commercial requirements.

In this situation, the object of the present invention is to provide ablock and method of making it economically and in large quantities, saidblock being superior as to internal stability, high uniform densitythroughout, and so much tougher than any solid carbon dioxide block everbefore produced as to amount to a new order of toughness, said toughnessresulting from a novel form of crystalline structure.

The block which we produce is diflicult to describe because it is unlikeanything of which we have knowledge. Its exterior, when free from frostof the atmosphere, appears somewhat like polished, more or lesstranslucent, white, or cloudy agate or even more like a perfect,uncracked cake of camphor ice. Its interior or fracture surfaces appearsomewhat like those of camphor ice and alum but differing from either asnoticeably as they differ from each other.

All tests that can be applied externally or to the fracture surfacesshow the internal structure to be substantially solid and free fromthroughextending voids or pores such as would permit internalevaporation and out-drainage of gas. One indication of this is thatfrost from the air forms on the surfaces at a much slower rate and ischaracteristically different in appearance and formation to that formedon the standard commercial blocks, the frost deposit being relativelysmooth except for slight ridges along scattered lines where surfacechilling of the block may have caused slight superficial check marks.These checks, when formed are characteristic, being entirely superficialand extremely minute, so that they do not materially increase theevaporation rate or the structural stability, strength or toughness ofthe block as a whole. Sometimes traces of impurities such as iron, beingfrozen out of the crystals, are visible as a slight veining effect.

We have discovered that these novel qualities, particularly the extra)rdinary toughness of our blocks, result not merely from decreasing thevoids and eliminating the through extending pores, but also, and moreimportant, from novel methods of recrystallization such that the blockconsists in large part, of relatively large fernlike crystals ofsubstantial length, that are intermeshed, interlocked and solidly bondedas by plate welding, probably by amorphous solid carbon dioxide. We uselong crystals for making our block and they appear laminated and quiteflexible, so the tensile strength and flexibility of large individualcrystals that appear in the block are likely to be important factors ofits strength and toughness. Such a block is fundamentally difierent fromthe standard blocks wherein the voids are great and the structuralstrength depends on the point welding between minute crystals. Thecrystals as they appear on the fracture surfaces of our product are ofrelatively large size, say to A inch in length and sometimes some ofthem are very much longer than this.

In the preferred embodiments of the invention, a 10-inch cube may weighover 50 pounds as against the 40 pounds for the standard commercialblock above described, and it can be subjected to shocks and mishandlingwithout damage, that would completely shatter the ordinary commercialblock. The less perfect embodiments of our invention may varyconsiderably in all of the above respects.

While some of the qualities of our product are distinguishableindependently of the method of making, the best way and possibly theonly way of making the preferred embodiments is by employment of theprinciples of our present method.

Whereas the prior art discloses no method of making crystals andnecessarily no method of making dense blocks of solid carbon dioxidefrom crystals except the application of great pressure, we havediscovered that in practice, time and heat may be made of equal orgreater importance and that the size of the crystals to be compressed isso important as to constitute a distinct part or branch of our genericinvention.

One point in the preferred method is to apply a pressure great enoughfor a time long enough or in a mold warm enough to cause adequatemelting of the solid carbon dioxide and flow thereof to the interior ofthe mass of crystals being compressed, under such conditions that itwill there recrystallize, mostly filling, but in any event completelysealing all voids; the recrystallizing being not in separate or minutecrystals and not merely as welds but as a substantial growth of theoriginal crystals or fragments thereof. That this actually takes place,under conditions which we establish, is evident from the fact that whenminute crystals are mixed with the large ones, the minute crystalsdisappear and samples are frequently produced in which breakage of largecrystals and recrystallizing of smaller ones, has resulted in averynoticeable tendency to uniform sizes, mostly about inch to inch inlength.

One discovery as to this part of our invention is that where thecrystals are made to exceed a certain size, and particularly where theyinclude a substantial percentage of crystals of very large size, theresistance to compacting of the crystals under pressure in the mold, isdecreased. It would seem that the large crystals afford far fewer andprobably larger areas of contact, so that they slip, break and compacteasily. Because of the enormously decreased number of contact surfaces,total pressure effective on each of the individual.points or surfaces isgreatly increased, so that it becomes possible with commerciallyattainable pressures applied for a reasonably short time, in a mold nottoo warm, to partially liquefy the solid, fill up and seal the voids,recrystallize the liquid, partly as growth of the larger crystalfragments and partly as amorphous bonds, so as to effectively unify amass of the crystals suflicient to make a tough solid block ofcommercial thickness yet of substantially uniform great density fromsurface to center.

If the crystals employed average large enough to ensure relatively fewcontacts, breakage under pressure will not multiply the contacts enoughto decrease individual contact pressures below the limit required forthe results above described.

Crystals of proper size for commercial practice of our methods may bemade by properly regulated, slow freezing of the liquid, as by applyingan external refrigerant to the liquid as in various prior patents suchas Josephson 1,659,431; or, preferably, by methods utilizing theprinciples of self intensive cooling by exaporation.

One method is to discharge high pressure liquid carbon dioxide into achamber in which is maintained a back pressure corresponding to thetriple point of carbon dioxide, approximately '15 pounds absolute persquare inch. Expansion of a certain amount of the liquid will reduce thechamber to triple point temperature and thereafter part of the liquidwill gasify, part will remain a liquid and part will freeze. In thissituation, the crystals of carbon dioxide will form and grow untilfinally all of the liquid is either crystallized or gasified. If thechamber is first charged with liquid at a pressure above the triplepoint, say '75 pounds absolute, the source then cut off and the backpressure in the chamber regulated down to the triple point, the liquidmay be boiled off as slowly as desired, giving the crystals any desiredamount of time for formation, the rate of gas released and time ofcrystallization determining how large the average size of the crystalswill be. Any suitable apparatus may be used for this purpose, as forinstance that disclosed in the patent to Jones, No. 1,877,180, to whichreference is hereby made for the details. For present purposes, the mainfeatures of the apparatus may be sufficiently understood from theaccompanying drawing, in which Fig. 1 is a diagram showing theessentials and following some of the details of the evaporator of saidapplication:

Fig. 2 is a diagrammatic view of a compressor that may be used to formthe block in accordance with the present method; and

Fig. 3 is a diagram showing a single chamber for both the evaporator andcompressor.

In Fig. 1 there is an exterior casing l of strength sufficient tosustain not only a triple point pressure of approximately '75 pounds,but a considerably higher pressure, which may be employed as a chargingpressure, say 150 pounds, plus a safety factor, or say, 500 pounds persquare inch. In the top of this casing is alarge manhole normallysecurely closed by a cover 2, which may be removed to insert a can 3,preferably suspended by the rim on ledges 4. This can is preferablyastight up to the level of outlets 5 which are provided for escape ofgas. These outlets may be guarded by a screen 6, which is preferablycarried by the manhole frame so that the can 3 may be lifted out andreplaced without disturbing it. The liquid carbon dioxide is suppliedthrough a pipe 7, which extends through the cover to discharge theliquid within the can 3. In the present case, we have diagrammaticallyindicated the discharge inlet as being an expansion nozzle 8, which maybe an ordinary snow making nozzle, although this is not essential. Thecasing is provided with an outlet 9, controlled by valve 10, whereby anydesired back pressure may be maintained within the casing 1 and therebyupon the inlet nozzle 8 and the surface of any liquid within the can 3.By adjusting the valve 10, the rate of escape of gas may be governed sothat liquid within the can 3 will be boiled off and crystallizedasslowly as may be desired, thereby insuring a desired average size forthe crystals, crystals of relatively enormous size being easilyattainable by sufficiently slow evaporation.

Almost any expansion or evaporator chamber could be used in this way, ifstrong enough to stand the. pressure, provided with the necessary valvesand arranged for removal of the crystals.

In Fig. 2, 11 is a mold in which the crystals may be compressed to forma block by means of a plunger 12, preferably operated by hydrauliccylinder 13 of known or desired type. The plunger applies the pressurethrough a follower 14 which may fit the mold loosely enough to permitescape of gas and air, at least until such time as the pressure becomessuflicient to form a more impervious seal of solid carbon dioxide. Thebottom of the mold may be integral, but in the present case we haveshown it as consisting of a follower pressure plate 15, like 14. Whenthis form is used it permits the block to be compressed within the moldby inward pressure at both ends so that for a given compression thecentral portion of the block does not have to slide on the walls,thereby reducing wall friction. Where large crystals are used, however,this friction is greatly reduced and a mold with an integral bottom maybe employed.

In Fig. 3, 21 is a chamber long enough so that it may be used first as acrystallizing chamber and then as a block-compressing chamber. As

in Fig. 1, it may be used for snow making and then for triple pointboiling, a liquid inlet and valve 22 and a gas outlet and back pressurevalve 23 being provided; preferably also a pressure gauge 24; also aplunger 12a of a hydraulic press operating a piston head 14a which isheld in the retracted position during crystal making. It is hereindicated as fitting closely but not gastight, although in the presentcase it may well be gas-tight because the crystals formed in the chamber21 do not contain any undesirable air and the pure gas in the voids ofthe crystals may be compressed, liquefied and frozen in situ. This formof apparatus, however, makes possible another feature of our method,which consists ofa final step after the crystal forming has beencompleted which consists in completely releasing the pressure and thenturning the valve 23 to conmeet with a vacuumizing conduit 23a. In thisway the sublimating point of the crystals may be lowered, therebyreducing the internal temperature from, say, -110 F. down to 140 F. or-150 F. As explained below, such subcooling of crystals by vacuumaccomplishes in a better way the sub-cooling that is accomplished byair.

The chamber 21 is hermetically sealed at the bottom by a closure 15a,which may be a breech block of any known or desired type capable ofwithstanding the enormous pressures to be applied through thecompressing piston 14a and of being conveniently open for ejecting thefinished block.

This apparatus will be recognized as analogous to that shown in SlatePatent 1,643,590 and, as in said patent, the liquid may be charged in atthe bottom of the chamber and caused to follow the retreat of the pistonuntil it uncovers the vent outlet 23.

As to the factor of warmth of the mold, it is to be noted that although,the mold gets very cold, and may be insulated by collected frost orotherwise, it continues to absorb some heat from the atmosphere.Consequently, the length of time the material is compressed in the moldwill be a factor of the amount of heat that will be imparted to it bythe mold. This factor may be controlled in various ways and. in specialcases, special heating means or insulation, permanent or adjustable may'be employed.

In practice of our method, either with ap-. paratus shown in Figs. 1 and2 or'that shown in Fig. 3, the crystals are likely to vary greatly insize according to the time they remain beneath the surface of the liquidunder crystallizing conditions of temperature and pressure. Some of themmay be wide, thin leaves, 2'inches or more in length and quite flexible,while others I may be of smaller size, grading down to a small amount ofwhat we call popcorn snow. Conditions can be controlled to make thesizes and the proportions of the smaller sizes relatively to the largersizes, well within the limits required for the purposes herein setforth. In general, the smaller sizes should not be less than 100 mesh,that is, .01 inch. Itwill be realized that crystals as small as this arereally of very great size as compared with ordinary snow jet crystalsnow commonly employed. Even so, the percentage of smaller crystals mustbe limited in favor of larger ones if best results are to be secured.

We find that when we press such coarse crystals with suificientpressure, the time need not be objectionably long nor the moldobjectionably warm, in order to produce truly solid, uniform, tough,stable block of over 90 pounds per cubic foot density, regardless of thedistribution of the charge in the mold prior to pressing. The coarsecrystals behave as though they flow in the mold, but fine crystals donot.

An important factor seems to be low initial teperature of the crystalsin the interior of the mass. If they are exposed to the air or arevacuumized, the crystals sublimate and chill down to l20 to 150 F.,according to the percentage of effective air or of vacuum, as the casemay be. This is far below the normal freezing point of -110 F. andprobably still more below the freezing point under pressure in the mold.If the crystals are sufficiently subcooled, in this or any other way atthe time the great pressure is applied in the mold, minute fragments caneasily melt, but the large ones embody large refrigerant values,sufficient to condense gas and freeze liquid whether sucked in or drivenin through the passages that initially exist between the fragments orthat may be produced interiorly by the pressure.

Any well-known method of pressing may be employed that will applysufficient pressure, the preferred pressure, even for coarse crystalsbeing over 1,000 pounds per square inch for blocks 10 inches deep. Itwill be understood, however, that these pressures are given forillustration only as a smaller pressure may be caused to produce asimilar result if the time, amount of heating, sizes of crystals orthickness of the block are properly regulated to produce the desiredliquefaction and recrystallization. The structure of the product is thebest criterion of whether these have been properly coordinated.

To illustrate the desirable properties attained, it may be stated thatproducts made in identical apparatus and under the same identicalconditions as our product, but from finer crystals, are less uniform andgenerally lower, in density and very much more fragile, as judged by thebreakage in dropping the various products or tumbling them underidentical conditions. When ordinary snow is used, even the densestproducts show fracture surfaces that are snow white, very smooth, andfollow directions of pressure applied in the making. There is none ofthe jaggedness and crystalline cleavage displayed by our product.

The importance of uniform density, toughness, and stable structure instorage cannot be overemphasized since these factors have limited thecommercial practicability of the products of the prior art severely, andhave made it imperative that solid carbon dioxide be used within a dayor so after, it has been produced to avoid structural changes instorage.

Owing to its non-porous and dense nature, our product is relativelystable and less subject to these changes.

It is important to note that blocks pressed from crystals will not havecommercial structural strength and toughness unless the crystals are ofsufiicient length to enmesh and hold the mass together, and, in general,the crystals visible to the naked eye'in the finished product should beover 1%; inch and mostly over inch in length, although with very largecrystals in the product it is fair to suppose that others of them may beless than inch long without sacrificing all of the novel properties ofour product, because they are scattered among the large crystals,embedded in and bonded by the amorphous solid. While the densities ofthese component elements of the .block may be slightly different, it isevident that the distribution throughout the block is so uniform thatfor all practical purposes the densities and refrigerant values aresubstantially the same for usable pieces taken from any part of theblock.

While our product as ordinarily made is translucent to a marked degree,it is possible to increase the translucency and under special conditionsto get substantially transparent blocks. For instance, if the crystalsare either exposed to air sufiiciently or are evacuated in a closedmachine, they will be cooled by evaporation to a temperatureconsiderably below the normal freezing point of 110 F. and possibly aslow as 140 F. If these supercooled crystals are brought in contact withpure carbon dioxide gas, they are capable of condensing some of it toliquid by absorbing sensible heat. Similarly they will freeze liquidformed by great pressure and by warmth of the walls of the mold. Thiscondition exists when the block is pressed. If the initial temperaturewithin the block is low enough, it will be sufficient to solidify allthe residual liquid or gaseous carbon dioxide within the mass and therewill be no gas bubbles; if, as in Fig. 3, air is excluded and a highenough vacuum applied, the result will be an absolutely clear blockwithout any air bubbles.

Referring again to Figs. 1 and 3, there are several composite methods ofproducing and growing crystals. For instance, the liquid may bedischarged in the chamber through the ordinary snow jet, the gas outletbeing free so as to maintain a pressure near atmospheric, say 10 poundsabove atmosphere. After a desired amount of ordinary carbon dioxide snowhas thus been made, the pressure may be raised to the triple point ofpounds, or preferably, above it, say pounds or 100 pounds, so that thecarbon dioxide will be discharged into the chamber as a liquid to wetdown and preferably submerge the snow. Thereupon the supply may be cutoff and the liquid boiled off as slowly as may be desired to permit anydesired amount of recrystallizing or growing of the snow crystals duringevaporation of the liquid.

While theories as to the details of obscure internal phenomena ofrecrystallization are not essential to practice of our invention, suchof them as have been offered will be found helpful working hypotheses,regardless of their accuracy, and in this connection it seems desirableto note a theory as to sizes of crystals. Where ordinary snow crystalsare used, they are all so minute that no matter how much they may besub-cooled, their individual heat absorbing capacities remain minute andtheir individual heat absorbing areas per unit volume are corelativelygreat. Moreover the pores or passages between them become exceedinglyminute under pressure. Consequently, when gas and liquid formed by theheat of the mold is forced or sucked into these capillary passages allthecrystals are .available to absorb all of the surplus heat. The resultis that all of the heat of the penetrating gas or liquid is quickly usedup in the outermost layers of the block, and the entrances of the inwardpassages are quickly choked by refreezing of the inflowing gas andliquid, consequently the bonding of the crystals in the interior of theblock is almost entirely by such minutely localized heating and pointwelding as can be'efiected by plunger pressure. On .the other hand, thelarger the sizes of the crystals at the time they are compacting byslipping and breaking under pressure, the greater the heat absorbingcapacity and the less the heat absorbing area of, the individualcrystals and, although the number of inwardly extending passages is muchfewer, their average cross-section for easy flow of gas and liquid fromthe mold walls to the interior is correspondingly multiplied.Consequently, if the crystals are of large average size, the smallerones can be completely remelted and the voids filled without exhaustingthe heat absorbing capacity (refreezing ability) of the larger crystalsandfragments. theory would tend to explain why lagre sizes, and also whymixed sizes, are desirable and will assist the maker in selectingaverage sizes suitable for the thickness of the desired block andregulating all of the other factors above described as contributing tobest practice of our invention.

As an illustration, a quantity of crystals or mixed sizes, say, .01" to2.", sufficient for a 10" cube, subjected to pressure of 1800 pounds persquare inch, more or less, in a fairly warm mold,

produced a tough block having practically uniform density of over 96pounds per cubic foot, together with other above described novel detailsof appearance, fracture surfaces, frosting, low evaporation rate, etc.

We claim:

1. In a method of making blocks by compressing a mass of solid carbondioxide crystals, the step which includes freezing liquid carbon dioxideto produce crystals, the freeezing being 'at a regulated rate to effectthe production of a product characterized by the major portion thereofconsisting of crystals over inch in length; then breaking the crystalsand compressing them to form the block.

2. The method of making blocks by compressing carbon dioxide crystals,whichincludes subcooling aquantity of pre-formed crystals many of whichare of relatively great size and applying pressure sufiicient to producesubstantial recrystallization and solidification in regions distributedthroughout the block. I

3. The method of making blocks by compressing carbon dioxide crystals,which includes sub-cooling a quantity of the crystals to a temperaturesubstantially below their normal freezing point and applying pressuresufficient to produce substantial recrystallization and solidificationinregions distributed through \the block.

4. The method of making blocks by compressing carbon dioxide crystals,which includes subcooling a quantity of the crystals to a temperaturesubstantially below their normal freezing point and applying greatpressure to said mass in a mold substantially above said temperaturefor; a time sufficient to produce substantial recrystallization andsolidification in regions distributed throughout the block.

5. The method of making blocks by compressing pre-formed carbon dioxidecrystals, which includes vacuumizing a mixture of crystals of great-Such a ly different sizes to cause accelerated evaporation sufficient tosub-cool them to a desired extent and applying heat and pressure inamounts and for times corelated to the average size of the subcooledcrystals so as to produce substantial recrystallization andsolidification in regions distributed throughout the block.

6. The method of making blocks by compressing pre-formed carbon dioxidecrystals, which includes assembling a mixture of crystals of greatlydifferent sizes sub-cooled to a desired extent and applying heat andpressure in amounts and for times corelated to the average size of thecrystals so as to melt the smaller ones and. to produce substantialrecrystallization and solidification in regions dnstributed throughoutthe block.

7. The method of making solid carbon dioxide, which includes slowlyevaporating liquid from and at the triple point, breaking the mass thusformed, and pressing it in a mold to a density of 95 pounds or more percubic foot.

8. In combination, a source of liquid carbon dioxide under high pressureand means for controlling discharge thereof, a crystallizing chambertherefor capable of safely withstanding pressures substantially abovethe triple point of the liquid, a gas outlet and valve means foradjusting the same to impose desired back pressures near the triplepoint in said crystallizing chamber, a removable closure through whichthe crystallized products may be withdrawn, means for vacuumizing saidchamber and a piston for subjecting the crystals to high pressure insaid chamber.

9. In combination, a source of liquid carbon dioxide under high pressureand means for controlling discharge thereof, "a crystallizing chambertherefor capable of safely withstanding pressures substantially abovethe triple point of the liquid, a gas outlet and valve means foradjusting the same to impose desired back pressures near the triplepoint in said crystallizing chamber, a removable closure through whichthe crys-' tallized products may be withdrawn and a piston for ejectingthe product when the closure is removed.

10. In combination, a source of liquid carbon dioxide under highpressure and means for controlling discharge thereof, a crystallizingchamber therefor capable of safely withstanding pressures substantiallyabove the triple point of the liquid, a gas outlet and valve means foradjustingthe same to impose desired back pressures near the triple pointin said crystallizing chamber, a removable closure through which thecrystallized products may be withdrawn and means for vacuumizing saidchamber.

11. In combination, a source of liquid carbon dioxide under highpressure and means for conliquid, a gas outlet and valve means foradjusting the same to impose desired back pressuresnear the triple pointin said crystallizing chamber and a removable closure through which thecrystallized products may-be withdrawn and a piston for subjecting thecrystals to high pressure in said chamber.

CHARLES L. JONES. JOHN D. SMALL.

